Detonative cleaning apparatus

ABSTRACT

Apparatus and methods are provided for cleaning a surface within a vessel. An elongate combustion conduit extends from an upstream end to a downstream end associated with an aperture in a wall of the vessel and positioned to direct a shockwave toward the surface. A resilient member resiliently restrains the combustion conduit against recoil forces.

BACKGROUND OF THE INVENTION

(1) Field of the Invention

The invention relates to industrial equipment. More particularly, theinvention relates to the detonative cleaning of industrial equipment.

(2) Description of the Related Art

Surface fouling is a major problem in industrial equipment. Suchequipment includes furnaces (coal, oil, waste, etc.), boilers,gasifiers, reactors, heat exchangers, and the like. Typically theequipment involves a vessel containing internal heat transfer surfacesthat are subjected to fouling by accumulating particulate such as soot,ash, minerals and other products and byproducts of combustion, moreintegrated buildup such as slag and/or fouling, and the like. Suchparticulate build-up may progressively interfere with plant operation,reducing efficiency and throughput and potentially causing damage.Cleaning of the equipment is therefore highly desirable and is attendedby a number of relevant considerations. Often direct access to thefouled surfaces is difficult. Additionally, to maintain revenue it isdesirable to minimize industrial equipment downtime and related costsassociated with cleaning. A variety of technologies have been proposed.By way of example, various technologies have been proposed in U.S. Pat.Nos. 5,494,004 and 6,438,191 and U.S. patent application publication2002/0112638. Additional technology is disclosed in Huque, Z.Experimental Investigation of Slag Removal Using Pulse Detonation WaveTechnique, DOE/HBCU/OMI Annual Symposium, Miami, Fla., Mar. 16-18, 1999.Particular blast wave techniques are described by Hanjalić and Smajevicin their publications: Hanjalić, K. and Smajević, I., Further ExperienceUsing Detonation Waves for Cleaning Boiler Heating Surfaces,International Journal of Energy Research Vol. 17, 583-595 (1993) andHanjalić, K. and Smajević, I., Detonation-Wave Technique for On-loadDeposit Removal from Surfaces Exposed to Fouling: Parts I and II,Journal of Engineering for Gas Turbines and Power, Transactions of theASME, Vol. 1, 116 223-236, January 1994. Such systems are also discussedin Yugoslav patent publications P 1756/88 and P 1728/88. Such systemsare often identified as “soot blowers” after an exemplary applicationfor the technology.

Nevertheless, there remain opportunities for further improvement in thefield.

SUMMARY OF THE INVENTION

Accordingly, one aspect of the invention involves an apparatus forcleaning a surface within a vessel. An elongate combustion conduitextends from an upstream end to a downstream end associated with anaperture in a wall of the vessel and positioned to direct a shockwavetoward the surface. A resilient member resiliently restrains thecombustion conduit against recoil forces.

In various implementations of the invention, the resilient member maycouple the combustion conduit to the wall. The resilient member mayinclude a metal coil spring. The resilient member may include a tensionspring. The apparatus may include a number of movable supportssupporting the combustion conduit at a number of locations along alength of the combustion conduit. The supports may accommodatelongitudinal expansion and/or contraction of the combustion conduit. Thesupports may include a number of trolleys each having wheels engaging atrack on a support surface. The conduit may include a number ofseparable segments. Each of the segments may be supported atop a singleassociated one of the trolleys. The supports may include a number ofhangers.

Another aspect of the invention involves a method for cleaning a surfacewithin a vessel of a piece of industrial equipment. Fuel and oxidizerare introduced to a conduit. A reaction of the fuel and oxidizer isinitiated so as to cause a shockwave to impinge upon the surface. Arecoil force upon the conduit is essentially taken up by a resilientmember.

In various implementations of the invention, the resilient member maystore energy of the recoil as the conduit shifts from an initialposition to a recoiled position and then returns the conduit to theinitial position. The shift may be at least 0.01 m (e.g., 0.03-0.01 m).A user may shift the conduit as a unit along a support mechanism todisengage a downstream end of the conduit from the vessel.

The details of one or more embodiments of the invention are set forth inthe accompanying drawings and the description below. Other features,objects, and advantages of the invention will be apparent from thedescription and drawings, and from the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view of an industrial furnace associated with several sootblowers positioned to clean a level of the furnace.

FIG. 2 is a side view of one of the blowers of FIG. 1.

FIG. 3 is a partially cut-away side view of an upstream end of theblower of FIG. 2.

FIG. 4 is a longitudinal sectional view of a main combustor segment ofthe soot blower of FIG. 2.

FIG. 5 is an end view of the segment of FIG. 4.

FIG. 6 is a view of a conduit segment support trolley of the system ofFIG. 1.

FIG. 7 is a side view of an alternate combustion conduit.

Like reference numbers and designations in the various drawings indicatelike elements.

DETAILED DESCRIPTION

FIG. 1 shows a furnace 20 having an exemplary three associated sootblowers 22. In the illustrated embodiment, the furnace vessel is formedas a right parallelepiped and the soot blowers are all associated with asingle common wall 24 of the vessel and are positioned at like heightalong the wall. Other configurations are possible (e.g., a single sootblower, one or more soot blowers on each of multiple levels, and thelike).

Each soot blower 22 includes an elongate combustion conduit 26 extendingfrom an upstream distal end 28 away from the furnace wall 24 to adownstream proximal end 30 closely associated with the wall 24.Optionally, however, the end 30 may be well within the furnace. Inoperation of each soot blower, combustion of a fuel/oxidizer mixturewithin the conduit 26 is initiated proximate the upstream end (e.g.,within an upstreammost 10% of a conduit length) to produce a detonationwave which is expelled from the downstream end as a shock wave alongwith associated combustion gases for cleaning surfaces within theinterior volume of the furnace. Each soot blower may be associated witha fuel/oxidizer source 32. Such source or one or more components thereofmay be shared amongst the various soot blowers. An exemplary sourceincludes a liquified or compressed gaseous fuel cylinder 34 and anoxygen cylinder 36 in respective containment structures 38 and 40. Inthe exemplary embodiment, the oxidizer is a first oxidizer such asessentially pure oxygen. A second oxidizer may be in the form of shopair delivered from a central air source 42. In the exemplary embodiment,air is stored in an air accumulator 44. Fuel, expanded from that in thecylinder 34 is generally stored in a fuel accumulator 46. Each exemplarysource 32 is coupled to the associated conduit 26 by appropriateplumbing below. Similarly, each soot blower includes a spark box 50 forinitiating combustion of the fuel oxidizer mixture and which, along withthe source 32, is controlled by a control and monitoring system (notshown). FIG. 1 further shows the wall 24 as including a number of portsfor inspection and/or measurement. Exemplary ports include an opticalmonitoring port 54 and a temperature monitoring port 56 associated witheach soot blower 22 for respectively receiving an infrared and/orvisible light video camera and thermocouple probe for viewing thesurfaces to be cleaned and monitoring internal temperatures. Otherprobes/monitoring/sampling may be utilized, including pressuremonitoring, composition sampling, and the like.

FIG. 2 shows further details of an exemplary soot blower 22. Theexemplary detonation conduit 26 is formed with a main body portionformed by a series of doubly flanged conduit sections or segments 60arrayed from upstream to downstream and a downstream nozzle conduitsection or segment 62 having a downstream portion 64 extending throughan aperture 66 in the wall and ending in the downstream end or outlet 30exposed to the furnace interior 68. The term nozzle is used broadly anddoes not require the presence of any aerodynamic contraction, expansion,or combination thereof. Exemplary conduit segment material is metallic(e.g., stainless steel). The outlet 30 may be located further within thefurnace if appropriate support and cooling are provided. FIG. 2 furthershows furnace interior tube bundles 70, the exterior surfaces of whichare subject to fouling. In the exemplary embodiment, each of the conduitsegments 60 is supported on an associated trolley 72, the wheels ofwhich engage a track system 74 along the facility floor 76. Theexemplary track system includes a pair of parallel rails engagingconcave peripheral surfaces of the trolley wheels. The exemplarysegments 60 are of similar length L₁ and are bolted end-to-end byassociated arrays of bolts in the bolt holes of their respectiveflanges. Similarly, the downstream flange of the downstreammost of thesegments 60 is bolted to the upstream flange of the nozzle 62. In theexemplary embodiment, a reaction strap 80 (e.g., cotton orthermally/structurally robust synthetic) in series with one or moremetal coil reaction springs 82 is coupled to this last mated flange pairand connects the combustion conduit to an environmental structure suchas the furnace wall for resiliently absorbing reaction forces associatedwith discharging of the soot blower and ensuring correct placement ofthe combustion conduit for subsequent firings. Optionally, additionaldamping (not shown) may be provided. The reaction strap/springcombination may be formed as a single length or a loop. In the exemplaryembodiment, this combined downstream section has an overall length L₂.Alternative resilient recoil absorbing means may include non-metal ornon-coil springs or rubber or other elastomeric elements advantageouslyat least partially elastically deformed in tension, compression, and/orshear, pneumatic recoil absorbers, and the like.

Extending downstream from the upstream end 28 is a predetonator conduitsection/segment 84 which also may be doubly flanged and has a length L₃.The predetonator conduit segment 84 has a characteristic internalcross-sectional area (transverse to an axis/centerline 500 of theconduit) which is smaller than a characteristic internal cross-sectionalarea (e.g., mean, median, mode, or the like) of the downstream portion(60, 62) of the combustion conduit. In an exemplary embodiment involvingcircular sectioned conduit segments, the predetonator cross-sectionalarea is a characterized by a diameter of between 8 cm and 12 cm whereasthe downstream portion is characterized by a diameter of between 20 cmand 40 cm. Accordingly, exemplary cross-sectional area ratios of thedownstream portion to the predetonator segment are between 1:1 and 10:1,more narrowly, 2:1 and 10:1. An overall length L between ends 28 and 30may be 1-15 m, more narrowly, 5-15 m. In the exemplary embodiment, atransition conduit segment 86 extends between the predetonator segment84 and the upstreammost segment 60. The segment 86 has upstream anddownstream flanges sized to mate with the respective flanges of thesegments 84 and 60 has an interior surface which provides a smoothtransition between the internal cross-sections thereof. The exemplarysegment 86 has a length L₄. An exemplary half angle of divergence of theinterior surface of segment 86 is ≦12°, more narrowly 5-10°.

A fuel/oxidizer charge may be introduced to the detonation conduitinterior in a variety of ways. There may be one or more distinctfuel/oxidizer mixtures. Such mixture(s) may be premixed external to thedetonation conduit, or may be mixed at or subsequent to introduction tothe conduit. FIG. 3 shows the segments 84 and 86 configured for distinctintroduction of two distinct fuel/oxidizer combinations: a predetonatorcombination; and a main combination. In the exemplary embodiment, in anupstream portion of the segment 84, a pair of predetonator fuelinjection conduits 90 are coupled to ports 92 in the segment wall whichdefine fuel injection ports. Similarly, a pair of predetonator oxidizerconduits 94 are coupled to oxidizer inlet ports 96. In the exemplaryembodiment, these ports are in the upstream half of the length of thesegment 84. In the exemplary embodiment, each of the fuel injectionports 92 is paired with an associated one of the oxidizer ports 96 ateven axial position and at an angle (exemplary 90° shown, although otherangles including 180° are possible) to provide opposed jet mixing offuel and oxidizer. Discussed further below, a purge gas conduit 98 issimilarly connected to a purge gas port 100 yet further upstream. An endplate 102 bolted to the upstream flange of the segment 84 seals theupstream end of the combustion conduit and passes through anigniter/initiator 106 (e.g., a spark plug) having an operative end 108in the interior of the segment 84.

In the exemplary embodiment, the main fuel and oxidizer are introducedto the segment 86. In the illustrated embodiment, main fuel is carriedby a number of main fuel conduits 112 and main oxidizer is carried by anumber of main oxidizer conduits 110, each of which has terminalportions concentrically surrounding an associated one of the fuelconduits 112 so as to mix the main fuel and oxidizer at an associatedinlet 114. In exemplary embodiments, the fuels are hydrocarbons. Inparticular exemplary embodiments, both fuels are the same, drawn from asingle fuel source but mixed with distinct oxidizers: essentially pureoxygen for the predetonator mixture; and air for the main mixture.Exemplary fuels useful in such a situation are propane, MAPP gas, ormixtures thereof. Other fuels are possible, including ethylene andliquid fuels (e.g., diesel, kerosene, and jet aviation fuels). Theoxidizers can include mixtures such as air/oxygen mixtures ofappropriate ratios to achieve desired main and/or predetonator chargechemistries. Further, monopropellant fuels having molecularly combinedfuel and oxidizer components may be options.

In operation, at the beginning of a use cycle, the combustion conduit isinitially empty except for the presence of air (or other purge gas). Thepredetonator fuel and oxidizer are then introduced through theassociated ports filling the segment 84 and extending partially into thesegment 86 (e.g., to near the midpoint) and advantageously just beyondthe main fuel/oxidizer ports. The predetonator fuel and oxidizer flowsare then shut off. An exemplary volume filled the predetonator fuel andoxidizer is 1-40%, more narrowly 1-20%, of the combustion conduitvolume. The main fuel and oxidizer are then introduced, to substantiallyfill some fraction (e.g., 20-100%) of the remaining volume of thecombustor conduit. The main fuel and oxidizer flows are then shut off.The prior introduction of predetonator fuel and oxidizer past the mainfuel/oxidizer ports largely eliminates the risk of the formation of anair or other non-combustible slug between the predetonator and maincharges. Such a slug could prevent migration of the combustion frontbetween the two charges.

With the charges introduced, the spark box is triggered to provide aspark discharge of the initiator igniting the predetonator charge. Thepredetonator charge being selected for very fast combustion chemistry,the initial deflagration quickly transitions to a detonation within thesegment 84 and producing a detonation wave. Once such a detonation waveoccurs, it is effective to pass through the main charge which might,otherwise, have sufficiently slow chemistry to not detonate within theconduit of its own accord. The wave passes longitudinally downstream andemerges from the downstream end 30 as a shock wave within the furnaceinterior, impinging upon the surfaces to be cleaned and thermally andmechanically shocking to typically at least loosen the contamination.The wave will be followed by the expulsion of pressurized combustionproducts from the detonation conduit, the expelled products emerging asa jet from the downstream end 30 and further completing the cleaningprocess (e.g., removing the loosened material). After or overlappingsuch venting of combustion products, a purge gas (e.g., air from thesame source providing the main oxidizer and/or nitrogen) is introducedthrough the purge port 100 to drive the final combustion products outand leave the detonation conduit filled with purge gas ready to repeatthe cycle (either immediately or at a subsequent regular interval or ata subsequent irregular interval (which may be manually or automaticallydetermined by the control and monitoring system)). Optionally, abaseline flow of the purge gas may be maintained betweencharge/discharge cycles so as to prevent gas and particulate from thefurnace interior from infiltrating upstream and to assist in cooling ofthe detonation conduit.

In various implementations, internal surface enhancements maysubstantially increase internal surface area beyond that provided by thenominally cylindrical and frustoconical segment interior surfaces. Theenhancement may be effective to assist in the deflagration-to-detonationtransition or in the maintenance of the detonation wave. FIG. 4 showsinternal surface enhancements applied to the interior of one of the mainsegments 60. The exemplary enhancement is nominally a Chin spiral,although other enhancements such as Shchelkin spirals and Smirnovcavities may be utilized. The spiral is formed by a helical member 120.The exemplary member 120 is formed as a circular-sectioned metallicelement (e.g., stainless steel wire) of approximately 8-20 mm insectional diameter. Other sections may alternatively be used. Theexemplary member 120 is held spaced-apart from the segment interiorsurface by a plurality of longitudinal elements 122. The exemplarylongitudinal elements are rods of similar section and material to themember 120 and welded thereto and to the interior surface of theassociated segment 60. Such enhancements may also be utilized to providepredetonation in lieu of or in addition to the foregoing techniquesinvolving different charges and different combustor cross-sections.

The apparatus may be used in a wide variety of applications. By way ofexample, just within a typical coal-fired furnace, the apparatus may beapplied to: the pendants or secondary superheaters, the convective pass(primary superheaters and the economizer bundles); air preheaters;selective catalyst removers (SCR) scrubbers; the baghouse orelectrostatic precipitator; economizer hoppers; ash or otherheat/accumulations whether on heat transfer surfaces or elsewhere, andthe like. Similar possibilities exist within other applicationsincluding oil-fired furnaces, black liquor recovery boilers, biomassboilers, waste reclamation burners (trash burners), and the like.

FIG. 6 shows further details of the exemplary trolley 72 and tracksystem 74. The exemplary track system comprises a pair of parallelvertex-up right angle channel elements 140 (e.g., of steel) secured suchas by welding to mounting plates 142. The mounting plates are, in turn,secured to the floor 76 such as via bolts (not shown) in bolt holes 144.The exemplary trolley includes a structural frame 150 having a pair ofleft and right longitudinal members 152 and fore and aft crossmembers154. At the left and right sides of each crossmember, a wheel 156 ismounted on a depending bracket 158. The wheel periphery has a concavity(e.g., a right-angle V-groove 160) receiving the vertex of the rightangle channel elements 140. The exemplary trolley has means forsupporting the associated conduit segment and means for securing thesegment in place. The exemplary support means include a pair of fore andaft tube/pipe clamps 170 each positioned and supported by nuts 172 onassociated left and right threaded shafts 174 secured at their lowerends to the frame. The clamps 170 have a concave surface 176complementary to the exterior body surface of the associated conduitsegment to support the segment from below. The securing means comprisessimilar top brackets 180 also mounted to the shafts 174 and helddownward in place in compressive engagement with the segment via nuts182.

A number of options are available for using the trolleys. The individualsegments may be preassembled to their associated trolleys and rolledinto place along the track system, whereupon the segments may be securedto each other via their end flanges. Disassembly may be by a reverse ofthis process. The trolleys may also allow the combustion conduit to bemoved as a unit (e.g., if it is desired that the downstream portion ofthe conduit not be inserted into the furnace all the time).Additionally, as noted above, the trolleys may accommodate movement as aunit associated with longitudinal thermal expansion and/or with recoilduring discharge cycles while maintaining conduit segment alignment.

FIG. 7 shows an alternate system 200 wherein the combustion conduit 202is suspended from brackets 204 (e.g., as part of a free-standing supportstructure or secured to a ceiling or roof 206 of the facility). Such asystem may be particularly useful where the conduit is positioned highabove a facility floor. The exemplary system 200 navigates the conduit202 around environmental obstacles external to the furnace. Exemplaryobstacles include upper and lower tube bundles 210 and 212 between whichthe conduit passes. In the exemplary embodiment, the conduit iscircuitous to permit positioning of its outlet 214 in a position on thefurnace wall aligned with one of the two bundles. In such a situation, astraight conduit would be interfered with by the bundles. Accordingly,the conduit is provided with one or more curved sections 216 toaccommodate the bundles.

From upstream to downstream, the exemplary support system includes anupstream and an intermediate spring hanger 220 and 222 coupled toassociated conduit segments by turnbuckle systems 224 and 226. Exemplaryspring hangers are available from LISEGA, Inc., Newport, Tenn. In theexemplary embodiment, the spring hanger 222 may have substantiallyhigher capacity due to a higher static load at that location. Theparticular combination of hanger sizings may be influenced by therelative locations of the hangers along the conduit in view of massparameters of the conduit (e.g., center of gravity, mass distribution,and the like), strength parameters of the conduit (e.g., variousmodulus), and the location of any additional support. The exemplaryspring hangers serve as essentially constant-load hangers, withsupportive tensile force essentially constant over an operating range.One function of the vertical compliance afforded by the hangers is toaccommodate thermally-associated changes in the vertical position of theoutlet 214 relative to the ceiling surface 206 or other combustionconduit support structure. For example, thermal expansion of the furnacewall may cause a change in outlet vertical position between hot and cold(e.g., running and off) furnace conditions. In the embodiment of FIG. 2,such expansion is addressed by non rigid vertical coupling of theconduit and wall with sufficient vertical play for the conduit withinthe oversized wall aperture. With rigid mounting, however, if furnaceheating raises the conduit outlet height, in the absence of the constantforce hangers, a greater fraction of the conduit mass would be carriedby the furnace wall and a lesser fraction by the upstream supports. Thiswould be associated with shear/bending forces/moments and associateddeformations. The spring hangers, however, will tend to contract,raising the segment(s) to which they are attached to so that the masssupported by the furnace wall does not substantially increase and thusto at least partially, and advantageously in major part, relieve/preventstresses that otherwise would be associated with the outlet elevationincrease, the hangers may, therefore maintain an essentially constantorientation of the conduit (e.g., maintaining its upstream major portionin an essentially horizontal orientation).

In the exemplary embodiment, a support structure 240 external to thecombustion conduit further reinforces the associated assembled segments.Such reinforcement advantageously handles structural stresses associatedwith shock reflections occurring within the curved segments. In theillustrated embodiment, the structure further rigidly ties downstreamportions of the conduit to the furnace wall. In the exemplaryembodiment, the turnbuckle 226 is connected via its lower threaded rodto a fixture 242 secured to the upstream end of the support structureand having snubbers 244 to accommodate and dampen side-to-side motion ofthe conduit which may arise from the combustion process. In theexemplary embodiment, the rigid connection of the support structure tothe furnace wall absorbs the recoil forces, essentially preventingrecoil. To the extent that longitudinal thermal expansion of the conduitremains an issue, such expansion may be taken up by allowing the hangersto pivot (e.g., relative to connection locations 246 to the brackets 204above and the connection point 248 with the associated conduitengagement fixture below. Alternative embodiments may remove the rigidcoupling of the conduit to the wall and permit a resilient or dampedcoupling.

One or more embodiments of the present invention have been described.Nevertheless, it will be understood that various modifications may bemade without departing from the spirit and scope of the invention. Forexample, the invention may be adapted for use with a variety ofindustrial equipment and with variety of soot blower technologies.Aspects of the existing equipment and technologies may influence aspectsof any particular implementation. Accordingly, other embodiments arewithin the scope of the following claims.

1. An apparatus for cleaning a surface within a vessel, the apparatuscomprising: an elongate combustion conduit extending from an upstreamend to a downstream end associated with an aperture in a wall of thevessel and positioned to direct a shock wave toward said surface; and aresilient member resiliently restraining the combustion conduit againstrecoil forces.
 2. The apparatus of claim 1 wherein: the resilient membercouples the combustion conduit to the wall.
 3. The apparatus of claim 1wherein: the resilient member comprises a metal coil spring.
 4. Theapparatus of claim 1 wherein: the resilient member comprises a tensionspring.
 5. The apparatus of claim 1 further comprising: a plurality ofmovable supports supporting weight of the combustion conduit at aplurality of locations along a length of the combustion conduit.
 6. Theapparatus of claim 5 wherein: the plurality of supports accommodatelongitudinal expansion and/or contraction of the combustion conduit. 7.The apparatus of claim 5 wherein: the plurality of supports comprise aplurality of trolleys each having wheels engaging a track on a supportsurface.
 8. The apparatus of claim 7 wherein: the combustion conduitcomprises a plurality of separable segments; and each of the segments issupported atop a single associated one of the plurality of trolleys. 9.The apparatus of claim 5 wherein: the plurality of supports comprise aplurality of hangers.
 10. A method for cleaning a surface within avessel of a piece of industrial equipment, the vessel having a wall withan aperture therein, the method comprising: introducing fuel andoxidizer to a conduit; and initiating a reaction of the fuel andoxidizer so as to cause a shock wave to impinge upon the surface, arecoil force upon the conduit being resiliently taken up by a resilientmember.
 11. The method of claim 10 wherein: the resilient member storesenergy of the recoil as the conduit shifts from an initial position to arecoiled position and then returns the conduit to the initial position.12. The method of claim 11 wherein: the shift is at least 0.01 m. 13.The method of claim 10 further comprising: shifting the conduit as aunit along a support mechanism to disengage a downstream end of theconduit from the vessel.